1. Field of the Invention
This invention relates to a magnetic bubble device in which the operating margins of magnetic bubble (hereinafter referred to as the bubble) stable operation regions of respective functional parts of the device are made nearly equal to provide for improved operating margin of the entire device.
2. Description of the Prior Art
In a magnetic bubble device, the bubble is merely propagated along a major or minor loop on the one hand and subjected to complicated control such that it is stretched out by a bubble detector on the other hand. In the former case of mere propagation the bubble remains in its normal shape and size, but in the latter case, the bubble stretches and becomes complex in shape. The bias field value for stable operation of the bubble differs in dependence on whether the bubble operates in its normal or stretched state. FIG. 1 is a graph showing how the bias field value differs, the abscissa representing the rotating-field intensity H.sub.R (Oe), and the ordinate the bias-field intensity H.sub.B (Oe). In FIG. 1, the margin curves of a bubble propagation path and a bubble stretcher are shown, and the area surrounded by each curve indicates a region of stable operation of the bubble. Accordingly, in the overlapping area of the both curves as indicated by hatching, the bubble stably operates regardless of whether it is on the propagation path or the stretcher. In FIG. 1, upper and lower straight lines show a collapse field H.sub.CO and a strip out field H.sub.so of a free bubble respectively, for the purpose of comparison. As is evident from FIG. 1, the upper limit of the bias field value of the region in which the bubble is stretched by a bubble detector, is lower than the upper limit of the bias field of the propagation path where the bubble operates in its normal state. The reason is that the presence of a strong bias field makes it difficult for the bubble to stretch long and hence prevents its smooth stretching and makes its operation unstable; therefore, the bias field value is inevitably selected, to be small for stable and smooth operation of the bubble.
In the case where the operating margins differ among different functional parts in the same magnetic bubble device, as described above, the overall operating margin of the device becomes very narrow, as indicated by the hatched region. Apart from a single-chip package, in the case of mounting a plurality of chips on the same package, variation in the operating margins of the chips further reduces the operating margin of the package as a whole.